It is not easy to measure currents accurately and over large dynamic ranges.
The most common method of current sensing is to pass the current through a resistor (a current shunt) and to measure the resulting voltage drop, which develops according to Ohm's law. A well-known current sensor circuit based on this principle is illustrated in FIGS. 1a, 1b, and 1c. 
Input terminals 3/3a and 4/4a allow connection of the current shunt 1 into the circuit where current has to be measured. FIG. 1a, as an example, shows that the actual connection points on the input terminals are simple holes 3a and 4a to which properly terminated power cable can be attached, both electrically and mechanically, by means of bolts and nuts or other suitable fasteners. This configuration is typical of current sensors capable of measuring several tens to several hundreds of Amperes.
An electronic circuit (omitted for clarity in FIG. 1a) measures voltage across the current shunt 1, via the sense lines 9 and 10; the actual current value is derived by the Ohm's law with the knowledge of the shunt's resistance.
Pick-up points 7 and 8 on the current shunt 1 follow the principle of “Kelvin sensing” that reduces errors associated with resistance of the sense connections and wires, considering the fact that there is almost no current in these sensing connections. The point made by “Kelvin sensing” is that because the current in lines 9 and 10 is extremely small, the voltage drop along lines 9 and 10 is likewise extremely small, and thus the voltage drop along lines 9 and 10 does not introduce very much error in the overall current measurement process. It will be appreciated that the pick-up points 7 and 8 are separate from and are specifically located apart from the main terminals 3a/4a of the shunt.
Typically, the shunt is created by joining three conducting sections with varying conductive properties. Sections 3 and 4 are made from highly conductive material (typically copper), and central section 2 is made from a material that has higher resistance as compared with that of copper, a material whose resistance has little or no dependence upon the magnitude of the current passing through the material, and the material having a resistance that has little or no dependence upon the temperature of the material. Some investigators choose this material to be “manganin”, an alloy of typically 86% copper, 12% manganese, and 2% nickel. The reasons for such a construction, among a few, include the desire to equalize the current density in the resistive material 2, and to minimize errors arising out of resistance variations due to magnitude of current or due to changes in temperature. The choice to have a central section differing in its material from end sections, and the choice of particular material for that central section, are outside of the scope of the present discussion, and as will later be appreciated, the teachings of the invention offer their benefits in ways that are not dependent upon such choices.
The thoughtful reader will appreciate that in the particular case where a shunt is selected to have such a central section 2 of non-identical material from the end sections, the shunt amounts to a thermocouple circuit, with the junctions of the thermocouples created by the joining of dissimilar materials in areas 5 and 6, and schematically depicted in the electrical model in FIG. 1(b). Temperature difference between areas 5 and 6 will create thermoelectric voltage on the sense lines 9 and 10; unfortunately, this voltage creates an error in the measured voltage across the shunt, and thus creates an error in the ultimate derived value for the measured current.
Furthermore, the attachment method of the sense lines 9 and 10 at points 7 and 8 may have a large effect on the total thermoelectric errors, as illustrated in FIGS. 1b and 1c. Typical sense lines 9 and 10 are made from copper and may, in fact, be simply traces on a printed circuit board (PCB). Connections to the current shunt at points 7 and 8 are typically made by soldering the sense lines to the shunt; solder material 7b in FIG. 1c is located between copper section 3 and sense line 9; at areas 7a and 7c this creates another pair of thermocouples. Any temperature difference between areas 7a and 7c will produce additional voltage errors.
The same considerations apply for the thermocouples created at junction 8 and shown schematically in FIGS. 1b as 8a, 8b, and 8c. 
Stating the situation in a different way and looking at FIG. 1b it is clear that thermoelectric voltages described above are connected in series with the voltage to be measured in element 2, thus giving rise to errors in the measured voltage and in the derived current value.
The designer of a shunt as shown in FIG. 1a must, of course, select locations 7 and 8 for the connection points for lines 9 and 10. Locations 7 and 8 will usually be selected to lie along a center line. Likewise nut-and-bolt connection points 3a and 4a will usually be selected to lie along the center line just mentioned. Finally, the designer of the shunt will usually be seen to design the shunt generally to have more or less reflective symmetry about the center line (to the left and to the right in FIG. 1a); usually this reflective symmetry is due not so much to any conscious choice as merely to simplicity and ease of manufacture.
The designer of the shunt as shown in FIG. 1a must also select locations 7 and 8 (vertically in FIG. 1a) along the center line. The usual design choice is to maximize the voltage output at sense lines 9 and 10 so as to maximize the signal-to-noise ratio for the sensed voltage. To maximize the voltage, the designer selects locations 7 and 8 to be farther apart from each other rather than closer together. The locations 7 and 8 are selected to be less far apart than nut-and-bolt connections 3a and 4a, but still quite far apart. It is not desired that location 7 be particularly nearby to point 3a and it is not desired that location 8 be particularly nearby to point 4a. 
It would be very desirable if apparatus could be devised which would reduce or eliminate errors in the derived current value that arise because of such thermoelectric voltages.